The formation of central synapses between appropriate partners requires local signals to allow some synaptic contacts to develop into stable synapses independently of others. This might be facilitated by local protein synthesis at synaptic endings; a process that contributes to activity-dependent changes in synaptic efficacy in the adult CNS. In this application we will test the hypothesis that appropriate cell-cell interactions target local acquisition of protein synthesis capabilities at developing synapses that contribute to the formation and long-term maintenance of synapses. Using cellular methods (electrophysiology, pharmacology, immunostaining and light and electron microscopy) and molecular techniques (RT-PCR, in situ hybridization and anti-sense methods), we plan to use a model cell culture system containing identified neurons of the marine mollusk Aplysia to examine the following aims: Aim 1: To determine whether local translation of exported mRNAs contribute to the formation of branch- and target-specific synapses. A) Does interaction with specific targets affect branch-specific distribution of exported mRNAs that encode molecules known to be critical for transmitter release? B) Are transported mRNAs translated at synaptic sites? C) Is local translation of mRNAs critical for the formation of synapses? Aim 2: To determine the role of intercellular signals in regulating local protein synthesis contributing to branch- and target-specific synapse formation. A) Are mRNA export and local protein synthesis regulated by expression and distribution of a cell adhesion molecule? B) Are mRNA export and local protein synthesis regulated by expression and release of secretory products, such as presynaptic neuropeptides or potential neurotrophic factors? Aim 3: To determine whether local protein synthesis is regulated by electrical activity that modulates synapse formation by competing inputs converging on a single target. A) Does asymmetric activity regulate targeting and distribution of mRNAs at active and inactive synaptic sites? B) Does asymmetric activity regulate local protein synthesis at active and inactive synaptic sites? The results of these studies will provide important information about how local interactions between neurons influence the development of behaviorally relevant neural Circuits and their specific connections.